A fuel injection system for supplying pressurized fuel to an internal combustion engine is provided. The fuel injection system includes a low-pressure hydraulic circuit, a fuel pump with a pumping element and an outlet valve for supply of pressurized fuel to a common rail, and an injector for delivering fuel for combustion from the common rail to the engine, wherein the fuel injection system further includes an isolating valve connected between the outlet valve of the fuel pump and the common rail, wherein the isolating valve is adapted such that the frequency of its seats making the mechanical contact with each other is lower compared to the frequency of the operation of the outlet valve of the fuel pump.